Semiconductor device and method for manufacturing same

ABSTRACT

A semiconductor device includes a first well and a second well provided within a semiconductor substrate, an isolation region disposed between the first well and the second well within the semiconductor substrate, a first wiring disposed on the first well, a second wiring disposed on the second well, a concave third wiring disposed on the isolation region, a buried insulating film disposed on the third wiring so as to fill the concave portion thereof, a plurality of fourth wirings disposed on the buried insulating film, and a contact plug disposed so as to electrically connect to at least one of the first and second wells.

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-171305 filed on Aug. 21, 2013, the disclosure of which are incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.

2. Description of the Related Art

In recent years, the miniaturization of semiconductor devices has made progress, thus resulting in a decrease in the equivalent oxide thickness (EOT) of a gate insulating film. Accordingly, a major increase in leakage current due to the decrease in the EOT has become problematic in a gate insulating film based on a silicon oxynitride film and a silicon oxide film, and a gate electrode structure made from polysilicon which have been used. Hence, an HKMG transistor is a focus of attention as a new technique to solve such a problem. The HKMG transistor is a transistor which comprises a gate insulating film including a high-dielectric insulating film higher in dielectric constant than oxide silicon, and a gate electrode including a metal layer. In the HKMG transistor, the high-dielectric insulating film is used for the gate insulating film, and therefore, gate leakage currents can be suppressed by increasing the physical thickness of the gate insulating film while decreasing the EOT. In addition, use of the gate electrode including the metal layer can improve the operating characteristics of the transistor.

JP2006-24594A and JP2007-329237A disclose the HKMG transistor.

A related method for manufacturing the HKMG transistor will be described with reference to FIGS. 26 to 28.

First, as illustrated in FIG. 26A, there is prepared semiconductor substrate 1 in which P well 3 and N well 4 are disposed through isolation region 2. A first laminated film including silicon oxide film 5 a, first high-dielectric insulating film 6 a, first metal film 7 a, and impurity-containing polysilicon film 8 a is formed on P well 3, and a second laminated film including silicon oxide film 5 b, first high-dielectric insulating film 6 b, second high-dielectric insulating film 6 c, first metal film 7 b, and impurity-containing polysilicon film 8 b is formed on N well 4. At this time, one end 10 a of the first laminated film and one end 10 b of the second laminated film are positioned on isolation region 2. In addition, trench portion 13 is formed of a side surface of end 10 a, a side surface of end 10 b, and a front surface of isolation region 2.

As illustrated in FIG. 26B, impurity-containing polysilicon film 11 and second metal film 12 are formed so as to extend in first direction 60 indicated above semiconductor substrate 1 from the space on P well 3 through the space on isolation region 2 to the space on N well 4. At this time, trench portion 13 cannot be completely filled with polysilicon film 11 and second metal film 12 since the aspect ratio of trench portion 13 is high, and therefore, seam 14 arises within trench portion 13. Under this condition, silicon nitride film 15 for use as a mask is formed on semiconductor substrate 1 by a plasma CVD method, so as to cover second metal film 12. At this time, silicon nitride film 15 fails to completely fill seam 14 since the plasma CVD method is inferior in coverage (step coverage), and therefore, seam 14 remains within silicon nitride film 15.

As illustrated in FIG. 27A, silicon nitride film 15 is patterned to form hard mask 15. The first and second laminated films and portions of polysilicon film 11 and second metal film 12 on isolation region 2 are patterned by etching using hard mask 15. Consequently, first and second gate electrodes 17 a and 17 b are formed on P well 3 and N well 4, respectively, and wiring 20 is formed on isolation region 2. LDD regions 19 a of the N conductivity type are formed within P well 3, and LDD regions 19 b of the P conductivity type are formed within N well 4. Offset spacers 26 a are formed on the side surfaces of first and second gate electrodes 17 a and 17 b and wiring 20. Thereafter, first source and drain 21 a of the N conductivity type are formed within P well 3, and second source and drain 21 b of the P conductivity type are formed within N well 4. SOD film 22 is formed on semiconductor substrate 1, and then CMP treatment or etched back of SOD film 22 is performed to expose hard mask 15. At this time, seam 14 remains as is within wiring 20, and second metal film 12 is exposed on the bottom of seam 14.

As illustrated in FIG. 27B, a contact hole to expose therein first source and drain 21 a is formed within SOD film 22. Thereafter, an electrically conductive material is formed so as to fill the contact hole, thereby forming contact plug 24 therein. At this time, seam 14 within wiring 20 is also filled with the electrically conductive material to form conductive part 20 a.

FIG. 28A is a plan view, and FIG. 28B represents a cross-sectional view taken along the A-A′ direction of FIG. 28A. As illustrated in FIGS. 28A and 28B, wirings 25 a and 25 b are formed on SOD film 22, so as to contact with hard mask 15. Here, wirings 25 a and 25 b are electrically connected to conductive part 20 a since conductive part 20 a has been formed in the process of FIG. 27B. As a result, the related method has been problematic in that wirings 25 a and 25 b short-circuit to each other through conductive part 20 a.

SUMMARY

In one embodiment, there is provided a semiconductor device comprising:

-   -   a first well and a second well provided within a semiconductor         substrate;     -   an isolation region disposed between the first well and the         second well within the semiconductor substrate;     -   a first wiring disposed on the first well;     -   a second wiring disposed on the second well;     -   a concave third wiring disposed on the isolation region;     -   a buried insulating film disposed on the third wiring so as to         fill a concave portion thereof;     -   a plurality of fourth wirings disposed on the buried insulating         film; and     -   a contact plug disposed so as to electrically connect to at         least one of the first and second wells.

In another embodiment, there is provided a method for manufacturing a semiconductor device, comprising:

-   -   preparing a semiconductor substrate including a first well, a         second well, and an isolation region between the first well and         the second well with respect to a first direction;     -   forming a first conductive film which is located on the first         well and one end of which in the first direction is positioned         on the isolation region, and a second conductive film which is         located on the second well and one end of which in the first         direction is positioned on the isolation region;     -   forming a third conductive film, so as to extend from a space on         the first conductive film through a space on the isolation         region to a space on the second conductive film with respect to         the first direction, and have a concave shape on the isolation         region;     -   forming a buried insulating film on the third conductive film,         so as to fill a concave portion of the third conductive film on         the isolation region;     -   patterning the first to third conductive films and the buried         insulating film to form a first wiring on the first well, a         second wiring on the second well, and a concave third wiring and         a buried insulating film on the isolation region;     -   forming an interlayer insulating film on the semiconductor         substrate;     -   removing a portion of the interlayer insulating film until the         buried insulating film is exposed;     -   forming a contact plug, so as to penetrate through the         interlayer insulating film, resulting in contacting with at         least one of the first and second wells; and     -   forming a plurality of fourth wirings, so as to contact with the         buried insulating film on the third wiring.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view illustrating a semiconductor device according to the first exemplary embodiment.

FIG. 2 is a cross-sectional view illustrating a semiconductor device according to the first exemplary embodiment.

FIG. 3 is a cross-sectional view illustrating a semiconductor device according to the first exemplary embodiment.

FIG. 4 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 5 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 6 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 7 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 8 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 9 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 10 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 11 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 12 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 13 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 14 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 15 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 16 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 17 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 18 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 19 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 20 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 21 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 22 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 23 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 24 illustrates a method of manufacturing a semiconductor device according to the first exemplary embodiment.

FIG. 25 illustrates a method of manufacturing a semiconductor device according to the second exemplary embodiment.

FIG. 26 illustrates a related method of manufacturing a semiconductor device.

FIG. 27 illustrates a related method of manufacturing a semiconductor device.

FIG. 28 illustrates a related method of manufacturing a semiconductor device.

In the drawings, numerals have the following meanings, 1: semiconductor substrate, 1 a: active region, 2: isolation region, 2 a, 52: silicon nitride film, 2 b, 51, 58 a, 58 b: silicon oxide film, 3: P well, 4: N well, 5 a, 5 b: silicon oxide film, 6 a, 6 b: hafnium oxide film (first high-dielectric insulating film), 6 c: aluminum oxide film (second high-dielectric insulating film), 7 a, 7 b: first metal film, 8 a, 8 b, 11, 11 a, 11 b, 11 c, 11 d: impurity-containing polysilicon film, 10 a, 10 b, 10 c, 10 d: end, 12, 12 a, 12 b, 12 c, 12 d: second metal film, 13: trench portion, 14: seam (concave portion), 15: silicon nitride film, 15 a: buried insulating film, 15 b: second insulating film, 15 c: first insulating film, 17 a: first gate electrode, 17 b: second gate electrode, 19 a, 19 b: LDD region, 20, 25 a, 25 b: wiring, 20 a: conductive part, 20′: third wiring, 21 a: first source and drain, 21 b: second source and drain, 22: SOD film, 24: contact plug, 25 c, 25 d: fourth wiring, 25 e: fifth wiring, 26 a: offset spacer, 26 b: sidewall spacer, 30: word line (buried gate electrode), 30′: dummy word line, 30 a: barrier metal film, 30 b: metal gate film, 31: bit line, 32 a: capacitor contact region, 32 b, 32 d: capacitor contact plug, 32 c: capacitor contact pad, 33: bit contact region, 37: third gate insulating film, 38 a: liner film, 38 b: SOD film, 39: bit contact interlayer insulating film, 43: liner film, 45: stopper film, 48: capacitor, 48 a: lower electrode, 48 b: capacitor insulating film, 48 c: upper electrode, 55: trench, 60: first direction, Cn: region for forming NMOS, Cp: region for forming PMOS, Tr1: first transistor, Tr2: second transistor, and Tr3: third transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes.

In one example of a semiconductor device and the manufacturing method thereof according to the present invention, a concave third wiring is disposed on an isolation region. In addition, a buried insulating film superior in coverage (step coverage) is formed so as to fill the concave portion of the third wiring. Consequently, even if a plurality of fourth wirings are formed on the buried insulating film, the third wiring and the fourth wirings are isolated from each other by the buried insulating film. Thus, it is possible to prevent a plurality of adjacent fourth wirings from short-circuiting to one another through the third wiring to degrade device characteristics.

Hereinafter, the semiconductor device and the manufacturing method thereof which are embodiments to which the present invention is applied will be described with reference to the accompanying drawings. Note that the drawings used in the following description are merely schematic, and length, width and thickness ratios and the like among respective drawings are not necessarily the same as actual ratios. Accordingly, length, width and thickness ratios and the like among respective drawings may not coincide with one another. In addition, conditions, such as materials and dimensions, specifically shown in the following embodiments are examples only.

Note that in the following embodiments, “first transistor” refers to an N-channel MOS transistor (hereinafter described as “NMOS” in some cases) formed in a peripheral circuit region, “Second transistor” refers to a P-channel MOS transistor (hereinafter described as “PMOS” in some cases) formed in the peripheral circuit region. “Third transistor” refers to a transistor formed in a memory cell region.

“First wiring” and “second wiring” respectively refer to first gate electrode 17 a formed on P well 3 and second gate electrode 17 b formed on N well 4 in the peripheral circuit region. “First well” and “second well” respectively refer to a P well and an N well. “First conductive film” refers to first metal film 7 a and impurity-containing polysilicon film 8 a formed on P well 3 of the peripheral circuit region (see, for example, FIG. 15). “Second conductive film” refers to first metal film 7 b and impurity-containing polysilicon film 8 b formed on N well 4 of the peripheral circuit region (see, for example, FIG. 15). “Third conductive film” refers to impurity-containing polysilicon film 11 and second metal film 12 (see, for example, FIG. 16).

First Exemplary Embodiment 1. Semiconductor Device

The present exemplary embodiment relates to a DRAM (Dynamic Random Access Memory) which is a semiconductor device to which a structure of the present invention is applied.

FIGS. 1 to 3 are schematic views illustrating the semiconductor device of the present exemplary embodiment, where FIG. 1A is a plan view of a memory cell region, FIG. 1B is a plan view of a peripheral circuit region, FIG. 2 is a cross-sectional view taken along the A-A′ direction of FIG. 1A, and FIG. 3 is a cross-sectional view taken along the A-A′ direction of FIG. 1B. Note that the plan views of FIG. 1 represent only major structures of the semiconductor device.

The DRAM of the present exemplary embodiment is composed of the memory cell region illustrated in FIG. 1A and the peripheral circuit region illustrated in FIG. 1B, and has a 6F2 cell layout (F denotes a minimum is processing size).

(Memory Cell Region)

As illustrated in FIG. 1A, a plurality of isolation regions (STI) 2 and a plurality of active regions 1 a are alternately formed at predetermined intervals in a Y direction in the memory cell region of the DRAM. Isolation regions 2 and active regions 1 a extend in an X′ direction shown in FIG. 1A. In addition, buried gate electrodes 30 to serve as word lines and dummy word lines 30′ extend in a Y direction, so as to come across active regions 1 a. Buried gate electrodes 30 and dummy word lines 30′ are formed as the result of being buried in semiconductor substrate 1 at predetermined intervals in an X direction. Yet additionally, a plurality of bit lines 31 is disposed at predetermined intervals in the X direction orthogonal to word lines 30 and dummy word lines 30′. A memory cell is formed in a region in which word line 30 and active region 1 a intersect with each other. Each memory cell is composed of third transistor Tr3 and an unillustrated capacitor. Third transistor Tr3 is composed of capacitor contact region 32 a and bit contact region 33 to serve as a third source and drain, word line 30, and an unillustrated third gate insulating film.

Word lines 30 and dummy word lines 30′ are the same in structure but different in functionality. Whereas each word line 30 is used as the gate electrode of third transistor Tr3, dummy word line 30′ is provided in order to isolate adjacent third transistors Tr3 from each other by applying a predetermined potential. That is, third transistors adjacent to each other on the same active region 1 a are isolated from each other by maintaining dummy word line 30′ at a predetermined potential and thereby turning off parasitic transistors. In addition, a plurality of memory cells are formed in the memory cell region as a whole, and a capacitor (not illustrated in FIG. 1A) is provided in each memory cell. Each capacitor is electrically connected to capacitor contact region 32 a through capacitor contact plugs 32 b and 32 d electrically connected to capacitor contact region 32 a of each transistor and through capacitor contact pad 32 c electrically connected to capacitor contact plugs 32 b and 32 d. As illustrated in FIG. 1A, capacitor contact plugs 32 b and 32 d are disposed at predetermined intervals within the memory cell region, so as not to overlap with each other. In addition, each memory cell is connected to bit line 31 through bit contact region 33.

As illustrated in FIG. 2, each memory cell is formed of third transistor Tr3 and capacitor 48 in the memory cell region. Third transistor Tr3 is composed of word line 30 formed of a buried gate electrode buried in semiconductor substrate 1, third gate insulating film 37 disposed between semiconductor substrate 1 and word line 30, and capacitor contact region 32 a and bit contact region 33 disposed on the principal surface of semiconductor substrate 1 to serve as a third source and drain. Each word line 30 is composed of, for example, barrier metal film 30 a made of a titanium nitride film and metal gate film 30 b made of a tungsten film. Each word line 30 is formed so that the upper surface thereof is lower than the upper surface of semiconductor substrate 1. Liner film 38 a made of a silicon nitride film and SOD (Spin on Dielectric) film 38 b are disposed on each word line 30.

Bit contact interlayer insulating film 39 made of a silicon nitride film is disposed on semiconductor substrate 1. A portion of bit contact interlayer insulating film 39 on bit contact region 33 is open, and bit line 31 is disposed in the portion, so as to contact with bit contact region 33. Bit line 31 is composed of, for example, impurity-containing polysilicon film 11 d and laminated film 11 e made of a tungsten nitride film and a tungsten film, in order from the side nearest to semiconductor substrate 1. Buried insulating film 15 a made of a silicon nitride film is disposed on bit line 31. Liner film 43 made of a silicon nitride film is disposed on bit contact interlayer insulating film 39 and on the side surfaces of bit line 31 and buried insulating film 15 a. SOD film (interlayer insulating film) 22 is disposed on liner film 43.

Capacitor contact plugs 32 b and 32 d are disposed so as to penetrate through SOD film 22, liner film 43 and bit contact interlayer insulating film 39 and connect to capacitor contact region 32 a. Capacitor contact pad 32 c is further disposed on SOD film 22, so as to connect to capacitor contact plugs 32 b and 32 d. Stopper film 45 made of a silicon nitride film and an interlayer insulating film (not illustrated) are disposed on SOD film 22, so as to cover capacitor contact pad 32 c. In addition, capacitor 48 is disposed so as to electrically connect to capacitor contact pad 32 c. Capacitor 48 is electrically connected to capacitor contact region 32 a through capacitor contact plugs 32 b and 32 d and capacitor contact pad 32 c. Note that capacitor contact pad 32 c may not be formed. In that case, capacitor 48 is formed on capacitor contact plug 32 d as appropriate. Capacitor 48 is formed as the result of lower electrode 48 a, capacitor insulating film 48 b and upper electrode 48 c being laminated in this order.

(Peripheral Circuit Region)

As illustrated in FIG. 1B, region Cn for forming an NMOS is formed and region Cp for forming a PMOS is formed are disposed in the peripheral circuit region. Regions Cn and Cp are disposed so as to sandwich an unillustrated isolation region (STI) therebetween. Active regions 1 a in which surfaces of semiconductor substrate 1 are exposed are disposed in regions Cn and Cp, and first gate electrode (first wiring) 17 a and second gate electrode (second wiring) 17 b formed simultaneously with the formation of bit lines 31 of the memory cell region are disposed so as to halve respective active regions 1 a. In region Cn, a high-concentration impurity is introduced into active regions 1 a on both sides of first gate electrode 17 a to convert the active regions into first source and drain 21 a. Likewise, in region Cp, a high-concentration impurity is introduced into active regions 1 a on both sides of second gate electrode 17 b to convert the active regions into second source and drain 21 b. First gate electrode 17 a, first source and drain 21 a, and an unillustrated first gate insulating film formed on region Cn constitute first transistor Tr1 in the peripheral circuit region. Likewise, second gate electrode 17 b, second source and drain 21 b, and an unillustrated second gate insulating film formed on region Cp constitute second transistor Tr2 in the peripheral circuit region. First source and drain 21 a is connected to fifth wiring 25 e through contact plug 24.

Third wiring 20′ is formed on the isolation region. A seam is present in the upper portion of third wiring 20′, thus causing the wiring to be concave-shaped. An unillustrated buried insulating film is disposed on third wiring 20′, so as to fill the seam (concave portion). Fourth wirings 25 c and 25 d are disposed on the buried insulating film. Third wiring 20′ and fourth wirings 25 c and 25 d are isolated from each other through the buried insulating film disposed on third wiring 20′. Consequently, it is possible to prevent fourth wirings 25 c and 25 d from short-circuiting to each other through third wiring 20′ to degrade device characteristics.

As illustrated in FIG. 3, the peripheral circuit region of the semiconductor device of the present exemplary embodiment includes P well 3 and N well 4. Isolation region 2 is disposed between P well 3 and N well 4 to insulate and separate P well 3 and N well 4 from each other. Isolation region 2 is composed of a laminated film made of silicon oxide film 2 b and silicon nitride film 2 a. Silicon oxide film 5 a and hafnium oxide film (first high-dielectric insulating film) 6 a serving as first gate insulating films are disposed on P well 3 in this order. Titanium nitride film (first metal film) 7 a, impurity-containing polysilicon films 8 a and 11 a, and first gate electrode (first wiring) 17 a composed of laminated film (second metal film) 12 a made of a tungsten nitride film and a tungsten film are disposed on the first gate insulating films. Silicon oxide film 5 b, hafnium oxide film (first high-dielectric insulating film) 6 b, and aluminum oxide film (second high-dielectric insulating film) 6 c serving as second gate insulating films are disposed on N well 4 in this order. Titanium nitride film (first metal film) 7 b, impurity-containing polysilicon films 8 b and 11 b, and second gate electrode 17 b composed of laminated film (second metal film) 12 b made of a tungsten nitride film and a tungsten film are disposed on the second gate insulating films. Buried insulating films 15 a are disposed on first and second gate electrodes 17 a and 17 b.

Concave third wiring 20′ is formed on isolation region 2. Third wiring 20′ is composed of impurity-containing polysilicon film 11 c and laminated film (second metal film) 12 c made of a tungsten nitride film and a tungsten film, where the upper portion of third wiring 20′ is concave-shaped. Buried insulating film 15 a superior in coverage (step coverage) is disposed so as to fill the concave portion of third wiring 20′. Offset spacer 26 a made of a silicon nitride film, sidewall spacer 26 b made of a silicon oxide film, and liner film 26 c made of a silicon nitride film are disposed in order on the side surfaces of first gate electrodes 17 a, second gate electrodes 17 b, and third wiring 20′, respectively.

LDD regions 19 a of the N conductivity type and first source and drain 21 a of the N conductivity type are respectively formed on both sides of first gate electrode 17 a within P well 3. LDD regions 19 b of the P conductivity type and second source and drain 21 b of the P conductivity type are respectively formed on both sides of second gate electrode 17 b within N well 4. P well 3, first gate insulating films 5 a and 6 a, first gate electrode 17 a, LDD regions 19 a of the N conductivity type, and first source and drain 21 a constitute the NMOS which is first transistor Tr1. In addition, N well 4, second gate insulating films 5 b, 6 b and 6 c, second gate electrode 17 b, LDD regions 19 b of the P conductivity type, and second source and drain 21 b constitute the PMOS which is second transistor Tr2.

SOD film (interlayer insulating film) 22 is disposed on semiconductor substrate 1 within the peripheral circuit region. Contact plug 24 is disposed so as to penetrate through SOD film 22 and connect to first source and drain 21 a. Fifth wiring 25 e is disposed on SOD film 22, so as to contact with contact plug 24, and fourth wiring 25 c is disposed so as to contact with buried insulating film 15 a on third wiring 20′.

2. Method for Manufacturing Semiconductor Device

Hereinafter, a method for manufacturing a semiconductor device of the present exemplary embodiment will be described with reference to FIGS. 1 to 23. Note that in FIGS. 4 to 11, 16 to 19 and 22 to 24, each view A represents a cross-sectional view corresponding to the A-A′ direction of the memory cell region in FIG. 1A, whereas each view B represents a cross-sectional view corresponding to the A-A direction of the peripheral circuit region in FIG. 1B. FIGS. 12 to 15 and 20 to 21 represent cross-sectional views corresponding to the A-A′ direction of the peripheral circuit region in FIG. 1B.

First, as illustrated in FIG. 4, isolation region (STI) 2 composed of a laminated film made of silicon oxide film 2 b and silicon nitride film 2 a is formed in the memory cell region and the peripheral circuit region within semiconductor substrate 1 (the isolation region is not illustrated in FIG. 4A). Consequently, active region 1 a divided off by isolation region 2 is defined in the memory cell region and the peripheral circuit region. In addition, P well 3 and N well 4 are formed within active region 1 a by a heretofore-known method. An impurity is implanted into semiconductor substrate 1 in the memory cell region to form an impurity-diffused layer. Subsequently, the principal surface of semiconductor substrate 1 is thermally oxidized to form silicon oxide film 51, and silicon nitride film 52 is formed on silicon oxide film 51. Silicon oxide film 51 and silicon nitride film 52 on the memory cell region are patterned to provide a hard mask pattern. Groove-like trench 55 extending in a direction intersecting with the isolation region is formed in semiconductor substrate 1 by etching using the hard mask pattern. This formation of trench 55 splits the previously-formed impurity-diffused layer into capacitor contact region 32 a and bit contact region 33 which are a third source and drain.

As illustrated in FIG. 5, the inner walls of trench 55 are oxidized by an ISSG (in-situ steam generation) method to form third gate insulating film 37 made of a silicon oxide film. Next, barrier film 30 a, such as a titanium nitride film, is formed on the inner walls of trench 55.

As illustrated in FIG. 6, trench 55 is filled with metal gate film 30 b, such as a tungsten film.

As illustrated in FIG. 7, the upper surfaces of barrier film 30 a and metal gate film 30 b are backed away from the principal surface of semiconductor substrate 1 by etch-back to form word line (buried gate electrode) 30. Consequently, there are formed capacitor contact region 32 a and bit contact region 33 to serve as a third source and drain, third gate insulating film 37, and third transistor Tr3 including word line (buried gate electrode) 30.

As illustrated in FIG. 8, liner film 38 a made of a silicon nitride film is formed on the entire surface of semiconductor substrate 1, and then SOD film 38 b is further formed thereon. Thereafter, a CMP treatment is performed on SOD film 38 b until the upper surface of liner film 38 a is exposed.

As illustrated in FIG. 9, upper portions of liner film 38 a and SOD film 38 b are removed by dry etching. Next, silicon nitride film 52 is removed by dry etching.

As illustrated in FIG. 10, bit contact interlayer insulating film 39 made of a silicon nitride film is formed on the entire surface of semiconductor substrate 1.

As illustrated in FIG. 11, bit contact interlayer insulating film 39 and silicon oxide film 51 deposited in the peripheral circuit region are removed in order using photolithographic and etching methods to expose the principal surface of semiconductor substrate 1.

Next, as illustrated in FIG. 12, the surfaces of P well 3 and N well 4 in the peripheral circuit region are thermally oxidized to form silicon oxide films 5 a and 5 b, respectively. Hafnium oxide film (first high-dielectric insulating film) 6 is formed on the entire surface of semiconductor substrate 1 by an ALD or CVD method. Thereafter, titanium nitride film (first metal film) 7 a, impurity-containing polysilicon film 8 a, and silicon oxide film 58 a are formed on the entire surface of semiconductor substrate 1.

As illustrated in FIG. 13, silicon oxide film 58 a is patterned using lithography and dry etching techniques to form a hard mask made of silicon oxide film 58 a, so as to cover P well 3. Polysilicon film 8 a and first metal film 7 a are dry-etched using hard mask 58 a. Consequently, a first conductive film made of first metal film 7 a and polysilicon film 8 a is disposed on P well 3. At this time, hard mask 58 a, polysilicon film 8 a, and first metal film 7 a deposited in the memory cell region are also removed at the same time.

As illustrated in FIG. 14, aluminum oxide film (second high-dielectric insulating film) 6 c is formed on the entire surface of semiconductor substrate 1 by an ALD or PVD method. Thereafter, titanium nitride film (first metal film) 7 b, impurity-containing polysilicon film 8 b, and silicon oxide film 58 b are formed on the entire surface of semiconductor substrate 1.

As illustrated in FIG. 15, silicon oxide film 58 b (not illustrated) is patterned using lithography and dry etching techniques to form a hard mask made of silicon oxide film 58 b, so as to cover N well 4. Polysilicon film 8 b, first metal film 7 b, hafnium oxide film 6 b, and aluminum oxide film 6 c are dry-etched using hard mask 58 b. Consequently, silicon oxide film 5 b, hafnium oxide film 6 b, aluminum oxide film 6 c, and a second conductive film made of first metal film 7 b and polysilicon film 8 b are disposed on N well 4. In addition, silicon oxide film 5 a, hafnium oxide film 6 a, and the first conductive film made of first metal film 7 a and polysilicon film 8 a are disposed on P well 3. At this time, silicon oxide film 58 b, polysilicon film 8 b, first metal film 7 b, hafnium oxide film 6 b, and aluminum oxide film 6 c deposited in the memory cell region are also removed at the same time to expose bit contact interlayer insulating film 39. At this point, one end 10 c each of hafnium oxide film 6 a and the first conductive film in first direction 60 is positioned on isolation region 2. Likewise, one end 10 d each of hafnium oxide film 6 b, aluminum oxide film 6 c, and the second conductive film in first direction 60 is positioned on isolation region 2. In addition, trench portion 13 is composed of ends 10 c and 10 d and isolation region 4.

As illustrated in FIG. 16, portions of bit contact interlayer insulating film 39 and silicon oxide film 51 on bit contact region 33 located in the memory cell region are removed using photolithographic and etching methods to expose bit contact region 33. In addition, hard masks 58 a and 58 b in the peripheral circuit region are removed by wet etching.

As illustrated in FIG. 17, impurity-containing polysilicon film 11 and laminated film (second metal film) 12 made of a tungsten nitride film and a tungsten film are formed on the entire surface of semiconductor substrate 1. At this time, polysilicon film 11 and second metal film 12 are formed in the peripheral circuit region, so as to extend from a space on the first conductive film through a space on isolation region 2 to a space on the second conductive film in first direction 60, as illustrated in FIG. 17B. Seam (concave portion) 14 arises above isolation region 2 of the peripheral circuit region since polysilicon film 11 and second metal film 12 are formed within trench portion 13 having high aspect ratio.

As illustrated in FIG. 18, silicon nitride film (buried insulating film) 15 a is formed on the entire surface of semiconductor substrate 1 by an ALD (Atomic Layer Deposition) method. Since silicon nitride film 15 a superior in coverage (step coverage) can be formed in the ALD method, it is possible to fill seam (concave portion) 14 with silicon nitride film 15 a. Next, silicon nitride film (second insulating film) 15 b is formed on silicon nitride film 15 a by a plasma CVD method. Whereas the ALD method is low in the rate of film formation, the plasma CVD method can achieve a high rate of film formation. Accordingly, it is possible to reduce the film-forming time of the silicon nitride films as a whole and improve throughputs, while filling seam 14 with silicon nitride film 15 a, by forming silicon nitride film 15 b by the plasma CVD method after silicon nitride film 15 a is formed by the ALD method.

As illustrated in FIG. 19B, silicon nitride films 15 a and 15 b are patterned using lithography and dry etching techniques to form hard masks made of silicon nitride films 15 a and 15 b on P well 3, N well 4 and isolation region 2 in the peripheral circuit region. Second metal film 12, polysilicon films 8 a, 8 b and 11, first metal films 7 a and 7 b, hafnium oxide films 6 a and 6 b, aluminum oxide film 6 c, and silicon oxide films 5 a and 5 b in the peripheral circuit region are dry-etched using the hard masks. Consequently, silicon oxide film 5 a and hafnium oxide film 6 a are formed on P well 3 as first gate insulating films, and first gate electrode (first wiring) 17 a including first metal film 7 a, polysilicon films 8 a and 11 a, and second metal film 12 a is also formed on the P well. Likewise, silicon oxide film 5 b, hafnium oxide film 6 b and aluminum oxide film 6 c are formed on N well 4 as second gate insulating films, and second gate electrode (second wiring) 17 b including first metal film 7 b, polysilicon films 8 b and 11 b, and second metal film 12 b is also formed on the N well. In addition, third wiring 20′ including polysilicon film 11 c and second metal film 12 c is formed on isolation region 2.

As illustrated in FIG. 19A, silicon nitride films 15 a and 15 b are patterned in the memory cell region simultaneously with the process of FIG. 19B to form a hard mask on bit contact region 33. Second metal film 12 and polysilicon film 11 in the memory cell region are dry-etched using the hard mask. Consequently, bit line 31 including polysilicon film 11 d and second metal film 12 d is formed on bit contact region 33.

As described above, hard masks made of silicon nitride films 15 a and 15 b are disposed on first and second gate electrodes 17 a and 17 b, third wiring 20′ and bit line 31.

As illustrated in FIG. 20, a silicon nitride film is formed on the entire surface of semiconductor substrate 1 and then etched back, thereby forming offset spacers 26 a on the side surfaces of first and second gate electrodes 17 a and 17 b and third wiring 20′. LDD regions 19 a are formed by implanting an impurity of the N conductivity type into P well 3 using hard masks 15 a and 15 b and offset spacer 26 a as masks. LDD regions 19 b are formed by implanting an impurity of the P conductivity type into N well 4 using hard masks 15 a and 15 b and offset spacer 26 a as masks.

As illustrated in FIG. 21, a silicon oxide film is formed on the entire surface of semiconductor substrate 1, and then a portion of the silicon oxide film deposited in the memory cell region is selectively removed using lithography and wet etching techniques. Thereafter, a portion of the silicon oxide film in the peripheral circuit region is etched back to form sidewall spacers 26 b on the side surfaces of first and second gate electrodes 17 a and 17 b and third wiring 20′. An impurity of the N conductivity type is implanted into P well 3 using hard masks 15 a and 15 b, offset spacers 26 a and sidewall spacers 26 b as masks to form first source and drain 21 a. An impurity of the P conductivity type is implanted into N well 4 using hard masks 15 a and 15 b, offset spacers 26 a and sidewall spacers 26 b as masks to form second source and drain 21 b.

As illustrated in FIG. 22, liner film 26 c made of a silicon nitride film is formed on the entire surface of semiconductor substrate 1, so as to cover first and second gate electrodes 17 a and 17 b and third wiring 20′ in the peripheral circuit region and bit line 31 in the memory cell region. A coating-based insulating film is formed on the entire surface of semiconductor substrate 1 and then anneal-treated to form SOD film 22.

Next, as illustrated in FIG. 23, a contact hole is formed so as to penetrate through SOD film 22, liner film 43, bit contact interlayer insulating film 39 and silicon oxide film 51 and expose capacitor contact region 32 a. After the contact hole is filled with a polysilicon film, the polysilicon film, silicon nitride film (not illustrated) 15 b and SOD film 22 are CMP-treated and planarized. At this time, silicon nitride film 15 b formed by a plasma CVD method is removed so that only silicon nitride film 15 a formed by an ALD method remains on first and second gate electrodes 17 a and 17 b, third wiring 20′ and bit line 31. In addition, the polysilicon film is etched back to recess the upper surface thereof, thereby forming capacitor contact plugs 32 b.

Next, as illustrated in FIG. 24, a contact hole is formed within SOD film 22 using lithography and dry etching techniques, so as to expose first source and drain 21 a. An electrically conductive material, such as tungsten, is filled in the contact hole to form contact plug 24. At this time, the electrically conductive material, such as tungsten, is also deposited on capacitor contact plug 32 b in the memory cell region, thus forming capacitor contact plug 32 d. Next, the conductive film made from tungsten or the like is patterned using lithography and dry etching techniques. Consequently, a plurality of fourth wirings are formed (see FIG. 1B only one fourth wiring 25 c is shown in FIG. 24B), so as to contact with silicon nitride film 15 a on SOD film 22 (third wiring 20′), and fifth wiring 25 e is formed so as to contact with contact plug 24. At this point, capacitor contact pad 32 c is formed at the same time, so as to contact with capacitor contact plug 32 d.

Subsequently, as illustrated in FIGS. 1A and 2, stopper film 45 made of a silicon nitride film and an interlayer insulating film (not illustrated) are formed so as to cover capacitor contact pad 32 c. A cylinder hole is formed so as to expose capacitor contact pad 32 c within the interlayer insulating film and stopper film 45, and then lower electrode 48 a is formed on the inner wall surfaces of the cylinder hole. Thereafter, the interlayer insulating film in the memory cell region is removed to expose the outer lateral surfaces of lower electrode 48 a. Capacitor insulating film 48 b is formed on the exposed surfaces of lower electrode 48 a, and then upper electrode 48 c is further formed so as to cover lower electrode 48 a and capacitor insulating film 48 b. Consequently, there is completed crown-shaped capacitor 48 composed of lower electrode 48 a, capacitor insulating film 48 b and upper electrode 48 c.

In the present exemplary embodiment, seam (concave portion) 14 of third wiring 20′ is filled with silicon nitride film (buried insulating film) 15 a. Accordingly, there is no such possibility that an electrically conductive material is filled in seam 14 in the process of forming a conductive film after the formation of the third wiring (the process of forming contact plug 24 and capacitor contact plug 32 d in the present exemplary embodiment). Consequently, third wiring 20′ can be prevented from electrically connecting to the plurality of fourth wirings. As a result, it is possible to prevent the plurality of fourth wirings from short-circuiting to one another through third wiring 20′ to degrade device characteristics.

Second Exemplary Embodiment

The present exemplary embodiment differs in that instead of the processes of FIGS. 17 and 18 in the first exemplary embodiment, silicon nitride film 15 c is formed by a plasma CVD method after polysilicon film 11 and second metal film 12 are formed and, thereafter, silicon nitride film 15 a is formed by an ALD method and silicon nitride film 15 b is formed by a plasma CVD method. The present exemplary embodiment is the same as the first exemplary embodiment except that the process of FIG. 25 is carried out instead of the processes of FIGS. 17 and 18 in the first exemplary embodiment, and therefore, only the process of FIG. 25 will be described here.

In the process of FIG. 25, silicon nitride film (first insulating film) 15 c is formed first by a plasma CVD method. Since this plasma CVD method is not superior in coverage (step coverage), it is not possible to completely fill seam 14 (concave portion) above isolation region 2 in the peripheral circuit region with silicon nitride film 15 c. It is possible to fill seam 14 (concave portion) above isolation region 2 with silicon nitride film 15 a, however, by subsequently forming silicon nitride film (buried insulating film) 15 a using an ALD method. Thereafter, silicon nitride film (first insulating film) 15 b is further formed by a plasma CVD method.

In the present exemplary embodiment, silicon nitride film 15 c is formed first by a plasma CVD method and, thereafter, silicon nitride film 15 a for filling seam 14 is formed by an ALD method. The plasma CVD method is higher in the rate of film formation than the ALD method. Accordingly, it is possible to further improve throughputs, compared with the first exemplary embodiment in which silicon nitride film 15 a is formed using the ALD method from the beginning until seam 14 is filled. Note that a plurality of films may be formed in seam 14 of third wiring 20′ by going through a plurality of film formation processes. In this case, at least one film formation process superior in coverage needs to be applied in order to completely fill seam 14 with a film. In other film formation processes, however, films inferior in coverage may be formed or films superior in coverage may be formed.

In the first and second exemplary embodiments, silicon nitride film 15 a is formed by an ALD method, in order to fill seam 14 above isolation region 4 in the peripheral circuit region. However, a film-forming method for filling seam 14 is not limited to an ALD method. Other film-forming methods may be used as long as the methods are superior in coverage and capable of filling seam 14. As such film-forming methods, it is possible to use, for example, a low-pressure CVD (LPCVD: Low-Pressure Chemical Vapor Deposition) method or a plasma CVD method lower in the rate of film formation than a plasma CVD method used in the first and second exemplary embodiments.

Third Exemplary Embodiment

The present exemplary embodiment differs from the first and second exemplary embodiments in that a silicon nitride film is formed by a plasma CVD method superior in coverage to fill the seam of the third wiring. More specifically, silicon nitride film 15 a is formed by a plasma CVD method superior in coverage in the process of FIG. 18 in the first exemplary embodiment. Alternatively, at least one of silicon nitride films 15 a and 15 b is formed by a plasma CVD method superior in coverage in the process of FIG. 25 in the second exemplary embodiment. Specific film-forming conditions for the CVD method to be superior in coverage are not limited in particular. It is possible to adjust film-forming conditions as appropriate, according to the properties of the seam of the third wiring. For example, a raw material gas is sufficiently supplied into the seam by increasing a source gas (SiH₄, NH₃ or the like) and decreasing a carrier gas (N₂ or the like) at the time of film formation, thereby performing film formation so that a film-forming reaction adequately takes place within the seam. In addition, RF high-frequency power is decreased at the time of film formation to lower the rate of film formation, thereby allowing a raw material gas to adequately reach the interiors of the seam. RF low-frequency power is slightly increased to improve the directionality of a source gas toward a substrate in which the third wiring is formed.

Also in the present exemplary embodiment, it is possible to form a buried insulating film superior in coverage (step coverage), so as to fill the concave portion of the third wiring. Consequently, it is possible to prevent a plurality of adjacent fourth wirings from short-circuiting to one another through the third wiring to degrade device characteristics.

In the first to third exemplary embodiments, first metal films 6 a and 6 b may be made of the same material or different materials. For example, in a case where different materials are used to set work functions separately for first metal films 6 a and 6 b, the NMOS may be composed of gate electrode which includes material other than a titanium nitride film, for example, a TaN, and the PMOS may be composed of a gate electrode containing a titanium nitride film. In addition, the gate electrodes of both MOS transistors may contain TiN and polysilicon, the gate electrode of the PMOS may contain Al, and the gate electrode of the NMOS may contain La or Mg. In a case where the same material is used for first metal films 6 a and 6 b, the same material, such as TiSiN, TaN or TiN, may be used for the gate electrodes of the NMOS and the PMOS to set work functions separately by varying the thicknesses of the electrodes.

The materials of the high-dielectric insulating films used in the first to third exemplary embodiments are not limited in particular, as long as the materials are higher in dielectric constant than oxide silicon. It is possible to use at least one insulating material selected from the group consisting of HfSiO, HfSiON, ZrO₂, ZrSiO, ZrSiON, Ta₂O₅, Nb₂O₅, Al₂O₃, HfO₂, ScO₃, Y₂O₃, La₂O₃, CeO₃, Pr₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃ and Lu₂O₃.

The second metal films used in the first to third exemplary embodiments are not limited in particular. In addition to the second metal films shown in the first to third exemplary embodiments, it is possible to use, for example, a laminated film composed of a tungsten silicide film, a tungsten nitride film and a tungsten film.

It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention. 

What is claimed is:
 1. A method for manufacturing a semiconductor device, comprising: preparing a semiconductor substrate including a first well, a second well, and an isolation region between the first well and the second well with respect to a first direction; forming a first conductive film which is located on the first well and one end of which in the first direction is positioned on the isolation region, and a second conductive film which is located on the second well and one end of which in the first direction is positioned on the isolation region; forming a third conductive film, so as to extend from a space on the first conductive film through a space on the isolation region to a space on the second conductive film with respect to the first direction, and have a concave shape on the isolation region; forming a buried insulating film on the third conductive film, so as to fill a concave portion of the third conductive film on the isolation region; patterning the first to third conductive films and the buried insulating film to form a first wiring on the first well, a second wiring on the second well, and a concave third wiring and a buried insulating film on the isolation region; forming an interlayer insulating film on the semiconductor substrate; removing a portion of the interlayer insulating film until the buried insulating film is exposed; forming a contact plug, so as to penetrate through the interlayer insulating film, resulting in contacting with at least one of the first and second wells; and forming a plurality of fourth wirings, so as to contact with the buried insulating film on the third wiring.
 2. The method for manufacturing a semiconductor device according to claim 1, wherein the buried insulating film is formed by an ALD method or a low-pressure CVD method in forming the buried insulating film.
 3. The method for manufacturing a semiconductor device according to claim 1, further comprising forming a first insulating film by a plasma CVD method between forming the third conductive film and forming the buried insulating film.
 4. The method for manufacturing a semiconductor device according to claim 1, further comprising forming a second insulating film on the buried insulating film by a plasma CVD method, following forming the buried insulating film.
 5. The method for manufacturing a semiconductor device according to claim 4, wherein the second insulating film is removed in removing the portion of the interlayer insulating film.
 6. The method for manufacturing a semiconductor device according to claim 1, further comprising, between forming the first to third wirings and the buried insulating film and forming the interlayer insulating film: forming a first source and drain on both sides of the first wiring within the first well; and forming a second source and drain on both sides of the second wiring within the second well, wherein a first transistor including the first source and drain and the first wiring as a first gate electrode is formed, and a second transistor including the second source and drain and the second wiring as a second gate electrode is formed.
 7. The method for manufacturing a semiconductor device according to claim 6, wherein the first transistor is an N-channel transistor, and the second transistor is a P-channel transistor.
 8. The method for manufacturing a semiconductor device according to claim 1, wherein the first well, the second well and the isolation region are located in a peripheral circuit region of the semiconductor substrate, the method further comprises: forming a third transistor including a third source and drain in a memory cell region of the semiconductor substrate, between preparing the semiconductor substrate and forming the first to third wirings and the buried insulating film; and forming a capacitor electrically connected to one of the third source and drain, following forming the fourth wirings.
 9. The method for manufacturing a semiconductor device according to claim 1, wherein the first conductive film includes a first metal film and an impurity-containing polysilicon film in order from the side nearest to the semiconductor substrate, and the second conductive film includes the first metal film and the impurity-containing polysilicon film in order from the side nearest to the semiconductor substrate.
 10. The method for manufacturing a semiconductor device according to claim 9, wherein the third conductive film includes the impurity-containing polysilicon film and a second metal film in order from the side nearest to the semiconductor substrate. 